1. Field of the Invention
This invention generally relates to wireless communications, and more specifically to communications systems that transfer data between a base station and a multiplicity of user stations.
2. Related Art
The state of the art for CDMA communications systems is substantially reflected in documents published by standardization bodies. The primary published standard that preceded the subject matter presented herein is identified as 3GPP2 C.S0002-C, “Physical Layer Standard for cdma2000 Spread Spectrum Systems,” published May 28, 2002, which is hereby incorporated in its entirety by reference. According to that standard, CDMA cellular communications devices may be enabled for high-speed packet data together with voice communication. Devices so enabled shall include a number of different physical channels. Although the method and apparatus presented herein were developed in this context, those skilled in the wireless communications art shall recognize that the improvements are applicable to other systems as well. A salient characteristic of such systems is their provision for packet data transfers between a base station and numerous mobile (or user) stations.
As is well known, cellular communications systems generally employ portable transceivers, each of which is called a mobile station (“MS”), for user communications. Such systems are one-to-many in nature, and generally include a relatively modest number of base stations (“BSs”) that each communicate with many MSs. The BSs are disposed as needed throughout geographical areas, to satisfy user demands for range and connection volume. For cellular systems providing high-speed packet data communications, the BS infrastructure must also satisfy user requirements for data volume.
Cellular system capacities are constrained by a variety of factors, such as the RF spectrum available to them, which limit the number of MSs that each BS can service. The economic value of a base station depends upon the number of MSs that can be concurrently served by the base station at a given level of quality of service. Thus, there is a need to increase the number of MSs that a base station is capable of serving, within system constraints based upon bandwidth availability and quality of service requirements.
To receive information accurately, wireless communications systems require an adequate signal-to-noise ratio (SNR). CDMA systems equivalently require a sufficient EC/I0 (energy per chip divided by the total energy within the spectral band used by the signal). With respect to a subject MS, the power of transmissions from its serving BS to other MSs appear as an increase in the total energy within the relevant spectral band, causing a decrease in the EC/I0 as measured by the subject MS. Thus, in the interest of increasing the number of MSs that can be served, and the rate of data transfer that can be provided, it is desirable for communications to take place at the lowest power levels that provide reliable operation.
Various efficiency-enhancing techniques have been implemented in cellular systems to help satisfy the need for high-speed data transmission at minimal power levels. For example, rather than transmit at a power that is sufficient to ensure accurate reception of every data packet, downlink data transmissions from a BS to an MS typically use an H-ARQ (hybrid automatic request for retransmission) procedure, whereby an MS will request retransmission when a particular packet is lost. Transmit power levels can thus be reduced until some packets are lost due to statistical noise variations. The resulting reduction in average transmission power levels frees capacity that may be used to accommodate additional users.
H-ARQ procedures may be implemented to improve an efficiency of high-speed data transfers on the reverse link (RL), whereby the BS will request retransmission from an MS in the event of a dropped packet. This imposes a requirement for a BS to acknowledge, on a forward link channel, data packets received from an MS. In order to conserve bandwidth, both in terms of transmission power and quantity of data overhead, the RL H-ARQ system needs to be efficient and reliable, which in turn requires that the forward link acknowledgement be maximally reliable with minimal transmission power requirements. In response to this need, a signaling method and apparatus is disclosed herein that may be implemented in a cellular communications system to improve the efficacy of cellular system RL data communications by reducing the overhead required to effect automatic retransmission.